Laser sintering (LS), also termed selective laser sintering, is a process whereby a dispenser deposits a layer of powdered material into a target area. A laser control mechanism, which typically includes a computer that houses the design of a desired article, modulates and moves a laser beam to selectively sinter the powder layer within the defined boundaries of the design. The control mechanism operates the laser to selectively sinter sequential powder layers, eventually producing a completed article comprising a plurality of layers sintered together.
More particularly, laser sintering generally is performed according to the following steps:
1. A piston of a process chamber is lowered by one layer thickness, and simultaneously, a piston of a cartridge containing a particulate material is raised;
2. The particulate material is introduced into the process chamber, and a leveling roller spreads the particulate material evenly over a build surface of the process chamber;
3. The particulate material then is heated to a temperature near, but below, its softening point;
4. A laser beam then traces a predetermined cross section of an article on the layer of heated particulate material in the build surface, thus forming a solid layer; and
5. Steps 2 through 4 are repeated until manufacture of a three-dimensional article is completed.
Particulate material in areas that have not been sintered by the laser remains unfused and in place, and acts as a natural support for the article being manufactured. Accordingly, no need exists for support structures during manufacture of the article. After cooling, the article of manufacture and the unfused particulate material are removed from the process chamber, and the article of manufacture is separated from the unfused particulate material, i.e., “breakout.” FIGS. 1 and 2 are schematics illustrating the LS process for the manufacture of an article having a complex shape. LS technology has enabled the direct manufacture of three-dimensional articles of high resolution and dimensional accuracy front a variety of materials including polymers and composite materials, such as polymer coated metals and ceramics.
A detailed description of LS technology can be found in U.S. Pat. Nos. 4,247,503; 4,863,538; and 5,017,753, each incorporated herein by reference. Clausen et al. U.S. Pat. No. 6,110,411, also incorporated herein by reference, provides a detailed description of the selective layer sintering process, and also discloses laser-sinterable thermoplastic compositions for use in the process.
Articles manufactured using LS technology can be rigid or flexible depending upon the identity of the particulate material used in the LS process. For example, if the particulate material contains a metal or a ceramic, the article is typically rigid. Flexible articles are prepared by an LS technique when polymeric materials such as those disclosed in WO 2005/025839 and U.S. Pat. No. 6,110,411 are used as the particulate material.
Both rigid and flexible articles manufactured by LS technology are sufficiently porous such that undesirable physical and esthetic properties can result. Porous articles having inadequate strength, unsatisfactory hardness, low abrasion resistance, and/or rough surface finish, are significantly limited with respect to the practical applications in which such articles can be used. Therefore, a method of improving the physical and esthetic properties of articles manufactured by LS technology remains a need in the art.
One means of achieving improved physical and esthetic properties is to infiltrate the article with a composition that at least partially fills the voids in the article. Infiltration is a long-practiced process to increase the strength of a porous material. However, prior infiltration methods and compositions have disadvantages, such as involving a complex procedure or altering the dimensions or physical properties of an article prepared by an LS process.
The present invention is directed to compositions and methods of infiltrating articles manufactured by an LS process that overcome the disadvantages associated with prior infiltration compositions and methods.